1. Field of the Invention
The present invention relates to an electrophoretic display device for executing a display utilizing electrophoresis of charged particles, and a method of producing an electrophoretic display device.
2. Related Background Art
There is already known an electrophoretic display device for executing a display utilizing an electrophoretic phenomenon of charged particles. In such device, an insulating liquid and charged particles are positioned between a pair of substrates of which at least either is transparent, and an electric field is applied therebetween by electrodes provided on either or both of the substrates to change a distribution of the charged particles, thereby performing a display. Such electrophoretic display device has the following advantages:    (a) the device has no dependence on polarizing characteristics or on a viewing angle, in contrast to the liquid crystal display;    (b) the device provides a bright display with a high utilization rate of light because of no use of polarizing plates;    (c) the device provides a non-light-emitting type passive display which is less tiring to the eyes in case of a prolonged observation, in contrast to light-emitting displays such as CRT, LED or EL; and    (d) the device is capable of rewriting a display with a low electric power consumption and it has a memory property, so that the electric power consumption is very little except for at the time of the rewriting display.
In such electrophoretic display device, it is necessary to prevent leakage of the insulating liquid.
Also in case of providing spacers for forming a uniform gap between the substrates or forming partition members for inhibiting a movement of the charged particles from a pixel to another pixel in order to prevent a display unevenness, an optical aperture rate is lowered to deteriorate the contrast or brightness of the display. Also unless a stable contact is secured between the substrate and the partition member, there cannot be avoided an unevenness in the thickness of the insulating liquid and an unevenness in time of a concentration of the charged particles.
Therefore, Japanese Patent No. 2551783 discloses a configuration of enclosing the insulating liquid and the charged particles in microcapsules and supporting such microcapsules between a pair of substrates (hereinafter called “Conventional Example 1”).
Also Japanese Patent Application Laid-Open No. 2000-35598 proposes, for positioning such microcapsules in desired positions, a method of supplying microcapsules one by one onto a surface of the substrate from a nozzle, utilizing an ink jet technology (hereinafter called “Conventional Example 2”).
Also Japanese Patent Application Laid-Open No. 2001-235771 proposes a method of discharging an insulating liquid by an ink jet method into a region surrounded by partition members on a surface of the substrate, and then bonding an opposed substrate to them (hereinafter called “Conventional Example 3”). Such method allows to separately supply the insulating liquids of different kinds to predetermined positions thereby enabling to produce a multi-color display device.
Such conventional examples have an advantage capable of preventing leakage of the insulating liquid, but are associated with a problem of an exact placing of a microcapsule in a position corresponding to a display electrode.
Also it is extremely difficult technically to securely supply the microcapsules one by one by the ink jet technology. Also in a large-sized high definition display panel, it becomes necessary to place an enormous number of microcapsules in predetermined positions, and the preparation of a display panel requires a long time by the method of supplying the microcapsules one by one from the nozzle.
Also the conventional examples have been associated with a problem of an inclusion or a bubble or a migration of the charged particles to another pixel, at the adhesion of the opposed substrate.